The present invention is generally related to the field of providing compensation control for a controlled apparatus which provides an output supplied to various associated output loads. More specifically, the present invention is related to predicting an expected output load change which is implemented in response to the closure of an electrical switch and altering a control input to the apparatus to provide compensation for the expected change (transient) in the output load condition. A particular application of the present invention relates to providing such load transient compensation for a vehicle internal combustion engine by sensing when various output loads are provided to the engine in accordance with the selective closure of various electrical switches.
Engine control systems for a vehicle are known in which, in an idle speed control mode, the extent of an expected change in engine load is predicted and the fuel mixture input to the engine is controlled in accordance with the expected engine load change so as to compensate for the load transient. This technique of predicting the occurrence of an engine load transient and providing compensation control to the engine in response to this prediction, rather than after and in response to the actual occurrence of a load transient, permits more accurate control of the engine. This is because the operating of the engine can be adjusted almost immediately at the start of a load transient rather than some time after the beginning of the load transient. Thus when an engine control system is, for example, implementing an idle speed control mode, prior systems have recognized that turning on vehicle accessories such as an air conditioner will provide a substantial additional engine load. Therefore in order to maintain the engine operating at a desired idle speed it is necessary to rapidly predict the occurrence and extent (magnitude) of this additional engine load and provide additional fuel and air to the engine substantially at the actual start of the air conditioner load transient. This will prevent an initial decrease in engine speed caused by the extra engine load provided by turning on the air conditioner.
In prior engine control systems such as those discussed above, typically the prediction of the occurrence and magnitude of a load transient is accomplished by directly coupling a plurality of various vehicle accessory turn on electrical switches as separate inputs to an engine control microprocessor. The microprocessor interrogates the operative state of each of these switches periodically or aperiodically and responds to the closure of these switches by altering the fuel mixture provided to the engine so as to provide for engine load transient compensation. Typically this is accomplished in an idle speed control mode for the engine control system since in that mode it is necessary to maintain the engine at a constant idle speed despite the occurrence of any selective addition or subtraction of various engine loads. If uncompensated for, these load changes could abruptly alter the engine idle speed. This altered idle speed would exist until the engine control system sensed the decrease or increase in idle speed or engine load provided in response to the engine load transient and then implemented a corrective adjustment of the engine fuel mixture or some other engine control parameter. Typically the adjustment of the engine fuel mixture is accomplished by either adjusting the amount of fuel being delivered to the engine and/or adjusting the amount of air being provided to the engine by an air bypass valve. Copending U.S. patent application No. 630,480 filed July 13, 1984 now abandoned and referred to above discloses an engine idle speed control system which implements idle speed control by controlling the engine fuel mixture in this manner.
In the prior engine control systems which predict engine load transients by having a microprocessor effectively interrogate the operative state of a number of accessory electrical switches directly connected as inputs to the microprocessor, relatively complex programming of the microprocessor is required to provide the desired end result. This occurs because the switch signals coupled as inputs to the microprocessor are two state digital signals and the microprocessor must then weight these digital signals in accordance with the magnitude of the engine load controlled by each switch, sum the weighted digital signals to determine the amount of load being provided in accordance with the closure of these switches, determine if a change (transient) in engine load has occurred which is of sufficient magnitude to justify implementing engine load compensation and calculate and implement the desired amount of engine load transient compensation. While such systems are certainly feasible, a key feature of such engine control systems is that they must rapidly respond to the closure of the switches so as to rapidly predict an expected change in engine load. By requiring extensive microprocessor analysis of the digital switch signals received from the switches, this reduces the response time of the engine control system and makes the system less able to rapidly respond to changes in engine load. This also requires utilization of a substantial amount of computer memory for storing the program which accomplishes the analysis of the digital switch signals. In addition, these prior systems require a number of direct digital signal inputs to the microprocessor thus increasing the number of input signal ports required for the microprocessor and thereby either increasing the cost of the microprocessor or eliminating the use of these input ports for receiving other sensor type information which may be needed.